This invention relates to a driving device used for fixing an anchor, or embedded thread structure, in a hole having an undercut at its bottom end; more specifically it relates to a driving device for an expansion sleeve which is a component of the anchor.
An object may be fastened to a hard surface, such as a concrete wall or ceiling, by first installing an anchor in the hard surface and then attaching the object to the anchor. Anchors have been proposed in the past, one of which is shown in FIG. 8. There, the anchor includes a tubular main or tension sleeve 1 having a hole with internal threads 4 and a groove 5 in its outer end surface for engagement by a screw-driver; an expansion sleeve 2 which has slits 6 cut into it lengthwise to form expansion pieces 7; and an embedded bolt 3 comprising a threaded part 9 at its upper end which is engaged with the threaded hole 4, and a conical surface 8 at its lower end.
The conventional procedure for using this structure is described as follows with reference to FIGS. 9a to 9d. A hole A which has an undercut part B is drilled into a concrete surface, and the bolt 3 and then the expansion sleeve 2 are inserted so that the expansion sleeve 2 rests lightly on the tapered surface 8 of the bolt 3 in the undercut part of the hole (FIG. 9a). Next, a tubular driving bar C having a cylindrical part the diameter of which is the same as the expansion sleeve 2, is inserted into the hole. The lower end of the driving bar C is placed against the outer end surface of the expansion sleeve 2, and then the head of the bar C is struck with a hammer F. The thin-wall joint 10 (FIG. 8) at the base (the upper end) of each expansion piece 7 of the expansion sleeve 2 is bent, and each expansion piece 7 is expanded along the protruding tapered surface 8 of the embedded bolt 3, thus firmly securing the bolt in the hole A (see FIG. 9b). Next, the main sleeve 1 is inserted into the hole, and its interior thread 4 is engaged with the threaded end 9 of the bolt 3 (FIG. 9c).
When the tip of a screwdriver is inserted into the screwdriver engaging groove 5 and the screwdriver is turned to screw the main sleeve onto the bolt 3, the main sleeve 1 is moved into contact with the outer end surface of the expansion sleeve 2, and the main sleeve 1 is thus fixed in the hole (FIG. 9c). In this way, the anchor is provided inside the hole A, and the outer internal thread 4 of the main sleeve 1 may be used to fasten a structure E to the concrete surface by means of a fixing bolt D (FIG. 9d).
However, because a manual force is used for the driving mechanism (the driving bar C and the hammer f) as mentioned above, a fairly large amount of labor is required, the driving takes some time, and it is difficult to attain a constantly uniform driving force. If the driving force on the expansion sleeve 2 is not uniform, the expansion sleeve 2 may not be securely press-set to the hole wall, sometimes resulting in the bolt 3 not being firmly fixed. If the bolt 3 is not firmly fixed, of course, the securing fixing cannot be attained for the structure E which is to be mounted afterward on the anchor.
It is a general object of this invention to provide a driving device with which the expansion sleeve can be driven in, easily and securely, by a specific amount and without excessive labor.